The invention relates to a fuel injection system for dosing and atomizing fuel under high pressure into an internal-combustion engine.
A fuel injection system has the functions, for each cylinder of an internal-combustion engine, to dose precisely the quantity of fuel supplied as a function of an operating state, to introduce the fuel into the combustion air at the correct time and to atomize the fuel sufficiently finely via the pressure gradient prevailing at an injection nozzle.
Such a fuel injection system is applicable to both diesel and Otto engines, to both single-cylinder and multiple-cylinder engines, and to both direct injection into the cylinder and suction pipe injection. The fuel injection system according to the invention is however intended preferably for diesel engines with direct injection under high pressure into each individual engine cylinder.
Numerous fuel injection systems are known. In the majority of known injection systems, a mechanically or hydraulically driven piston pump doses the fuel into the combustion air intermittently at a controllable ties pressurises it, and displaces it through the injection nozzle. The quantity of fuel injected in this case is varied by varying the delivery stroke of the piston of the piston pump (so-called stroke regulation), by varying the quantity of fuel in the pump chamber of the piston pump (so-called charge regulation), or by varying the throttle cross-sections effective during the delivery (so-called throttle regulation).
It is also known to provide a separate pump piston for each cylinder of the internal-combustion engine in a series of pumps or pump/injection nozzle combinations. Distributor pumps are also known, wherein a plurality of cylinders of the internal-combustion engine are alternatively supplied from one pump piston in the pump.
These known injection systems have a number of disadvantages. They require one or more intermittently driven pump pistons. The structural outlay for the pump piston drive is high due to the intermittent loading. Furthermore, the fuel pump must controllably time the delivery for variable speed operation. The structural outlay for this purpose is substantial.
Lastly, a fuel injection system is also known wherein a non-periodic fuel pump delivers fuel at regulated pressures into a system common to all the cylinders of the internal-combustion engine. The injection quantity is regulated by the fuel pressure and the time cross-section of the injection nozzle at each cylinder--i.e., the integral of the free flow cross-section of injection orifice over the time. It is therefore necessary to control precisely the time cross-section of each injection nozzle. This is performed either mechanically or electromagnetically.
Even the last-mentioned injection system has serious disadvantages. In order for the fuel pump to be able to deliver at regulated pressure, it must deliver more fuel than is required for the injection, and the control of the time cross-section of the injection nozzles necessitates a considerable structural outlay. Control of the injection quantity by means of the time cross-section becomes increasingly difficult, or even impossible, as the injection time becomes shorter.